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When the deadliest tsunami in recorded history devastated more than a dozen countries around the Indian Ocean on Dec. 26, 2004, few people knew what was happening. Almost none of them received any warning. Hundreds of thousands of them died.

But 10 years later, the legacy of the 2004 Indian Ocean tsunami is a beefed up, high-tech worldwide warning system and a keen public awareness of the threat posed by tsunamis that will save many lives in the future.

Indonesian Muslims in Jakarta weep during special prayers for victims of the quake-triggered tsunami in Aceh in 2004. More than 230,000 people died in the most deadly tsunami in recorded history. (Dadang Tri/Reuters)

Videos recorded shortly before the 2004 tsunami hit show people lounging on beaches in places like Thailand, oblivious to the threat posed by the roiling, white wall of water – a giant wave – barrelling toward the shore. If they'd received warning, they could have sought the safety of high ground. Instead, the disaster killed 230,000 people from Indonesia to Sri Lanka to Somalia, and left half a million people homeless.

Triggered by a magnitude 9.2 earthquake off the coast of Sumatra, the tsunami demolished buildings and washed away vehicles, putting entire villages and forests under several storeys of churning water filled with debris and struggling people. Along with the catastrophic loss of life, the disaster caused an estimated $13 billion in damage.

At that time, says Garry Rogers, a research scientist at the Geological Survey of Canada, very few people around the world even knew what a tsunami was.

That changed after video footage was broadcast on television: People around the world watched in fascinated horror as the frothing white waves leaped over bushes and balconies, swallowing up boats and people. A churning flood of brown water topped with half-submerged cars, broken furniture and massive tangles of wood planks from smashed buildings rushed inland through the streets and resorts of Indonesia and Thailand.

10th Anniversary of the Asian Tsunami1:47

Those images, and similar video from the 2011 Japan tsunami, raised keen public awareness of the danger of tsunamis, said Rogers.

"Almost everyone in the world now knows what a tsunami is and what it can do … that's made a huge difference in public policy."

Not only were people unaware of the tsunami threat in 2004, but they also received no warning. At the time, a limited tsunami warning system did exist, but only on the Pacific Ocean, where most tsunamis occur. There were no sea level gauges to detect a tsunami anywhere near Sumatra, for example. And even the detection of earthquakes was not as precise as it is today.

"In a sense, we were flying blind," said Stuart Weinstein, deputy director of the U.S. National Oceanic and Atmospheric Administration's Pacific Tsunami Warning Center, at a news conference organized by NOAA earlier this month.

Staff at NOAA's Pacific Tsunami Warning Centre didn't realize that the Indonesian earthquake had triggered a tsunami until about five hours later when staff read a Reuters news report that a tsunami had struck Thailand. (CBC)

The centre had received data about the earthquake minutes after it occurred, but had underestimated its magnitude. It did not realize the earthquake had triggered a tsunami until about five hours later, when staff read a Reuters news report that a tsunami had struck Thailand, Weinstein said.

Rogers added that even if warnings were issued by people monitoring for earthquakes and changes in sea level, at the time there weren't necessarily organizations in place in the countries around the Indian Ocean to receive the warning and pass it on to local authorities and residents.

Things have changed drastically since then. Very few people are now killed by tsunamis triggered by earthquakes on the other side of the ocean, Rogers says.

New systems in Atlantic, Indian Oceans

Since the 2004 disaster, new tsunami detection and warning systems have been installed around the world, including places like the Indian and Atlantic oceans that didn't have such systems before.

A sea-level gauge is a pressure sensor that measures weight to calculate the height of the water above it. Canada has the most precise such sensors in the world, says Kate Moran, president and CEO of Ocean Networks Canada. (Ocean Networks Canada)

Such detection systems consist of:

Seismometers that detect earthquakes that could trigger a tsunami, and communicate directly with tsunami warning centres.

Computer models that use data about past tsunamis and local geography to estimate the size of a potential tsunami and where and when it could strike.

Sea-level gauges on the ocean floor and tide gauges on shorelines to measure and communicate the speed and height of a tsunami as it takes place, which can be used to update tsunami warnings and refine the computer models.

Canada gets its warnings from the U.S. national tsunami warning system, and provides earthquake data in return. Since 2004, Rogers aid, Canada has boosted the number of stations providing live earthquake data over the internet from 10 to 30.

Meanwhile, the number of tsunami-detecting sea level gauges have gone from six to dozens around the world, provided by many different countries.

Such detectors typically consist of a pressure sensor that measures weight to calculate the height of the water above it. Most can detect changes as small as one centimetre. That's important because when a tsunami is out at sea, most of the wave is underwater and it's more spread out than when it approaches the shore. The sensors usually transmit data from a buoy on the surface via satellite to tracking centres.

'Almost everyone in the world now knows what a tsunami is and what it can do.'- Garry Rogers, Geological Survey of Canada

Canada has the most precise sea-floor pressure sensors in the world, capable of measuring differences of less than a millimetre, says Kate Moran, president and CEO of Ocean Networks Canada, a non-profit group that runs an undersea observatory off the west coast of B.C. The sensors, made by Kanata, Ont.-based RBR Ltd., are wired directly to the internet for faster communication to tsunami warning centres.

From 20 minutes to 5

The monitoring system's speed has been drastically increased. On-shore tide gauges around the world have been upgraded to transmit their data once a minute instead of once a month, for example.

Partly because of the sensor data, computer models of tsunamis have improved in the past decade, making predictions more precise.

And tsunami warning centres are now staffed around the clock, rather than on an on-call basis during off-hours, Rogers said.

Altogether, that means tsunami detection and warning times have gone from 20 minutes to five minutes or less in areas like Canada's west coast, Rogers said.

A man walks past a ship brought ashore by the December 2004 tsunami when it hit the Indonesian city of Banda Aceh. (Beawiharta/Reuters)

Even when the warning is issued in five minutes , that may still not be enough time to save people from tsunamis triggered by very nearby earthquakes. In that case, the only thing that may save lives is teaching people on the coastline to flee immediately to higher ground when there's an earthquake.

"Public education is probably the most important thing," Rogers said.

Tsunami warnings can also still take half an hour to issue in some parts of the world where there aren't enough seismographs to make faster predictions. That's one area where Rogers says improvements can be made.

Moran said better maps of the shape and depth of the sea floor could also refine tsunami models and make more precise local predictions about expected tsunami height.

For Canada, Rogers said, the current goal is to get tsunami warnings times down from five minutes to two.

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